This invention is directed generally to transmission controllers, and more particularly to an automated transmission control system which automatically calibrates the system for accommodating clutch starting torque for the associated transmission.
In relatively large on-the-road or off-the-road vehicles, relatively complex transmissions are required. Large heavy construction equipment, farm tractors and the like, generally employ transmissions which provide for multiple gears in both forward and reverse directions. Such multiple gearing systems commonly require multiple gear shift levers, multiple clutches, and corresponding operator controls for manual operation thereof. In addition, many such vehicles such as tractors, road construction or other construction equipment, etc., often require numerous other operator controls for controlling various accessories, such as blades, backhoes, buckets, farm implements, and the like.
Accordingly, it has been heretofore proposed to provide automated or partially automated transmission control systems for simplifying the manual operation of the vehicle transmission. Such control systems may employ solenoid operated valves which valves apply hydraulic pressure in a clutch cavity for operating the clutches of the transmission to free the operator from foot-pedal-operated or otherwise operator-actuated clutches. Such controls may also incorporate simplified shift levers which electrically or electro-hydraulically operate corresponding clutches and other mechanical components for engaging the desired gears without cumbersome manual operation of large heavy gear shift levers or the like by the operator.
Such control systems require relatively sophisticated electronic control arrangements for properly integrating the disengagement and reengagement of clutches and the selection of gears in the proper sequence and with the proper timing to assure smooth shifting of the transmission through both forward and reverse gears, and also from forward to reverse gears or vice versa, as may be desired in operation. It should be noted in this regard that such shifting is not always between adjacent gears. Operating conditions may require shifts from neutral which "skip over" a number of gears, or even shifts from a high forward gear to a reverse gear or vice versa.
One problem that has heretofore arisen in such transmissions is the problem of obtaining a smooth transmission operation during various vehicle operations. Such operations include starting the vehicle moving from a standstill, any forward to reverse shifting (or vice versa), certain gear shifts, and so-called feathering operations and/or inclining operations. Certain gear shifts sometimes occur between two gears which require engagement and disengagement of multiple clutches In order to smoothly shift between two gears which are employed using multiple clutches, it is important that the clutches be smoothly disengaged and engaged in synchronization to maintain a controlled clutch slippage for smooth shifting between the gears. The same sort of controlled slippage of clutches is also required in so-called feathering and inching operations, and during start up/slow down and/or directional changes. This requires that the controller be properly calibrated to, in effect, "feel" the engagement and disengagement of the respective clutches to insure a smooth transmission operation in the foregoing types of operations.
In our novel system, we use solenoid-actuated proportional valve-operated clutches. We have found that it is necessary that the solenoids be provided with controlled operating currents to assure proper operation of the proportional valves to obtain a smooth and synchronized engagement and disengagement of respective clutches during those types of operations in which controlled clutch slippage is required.
Heretofore it has been proposed to calibrate the proportional valves by manually adjusting the valves to obtain a given pressure when a known or given current is being applied to the associated solenoid. For example, a predetermined threshold current was applied to the solenoid while the corresponding proportional valve was adjusted to achieve a nominal operating clutch pressure of 50 psi. The desired result of this operation is to achieve a clutch pressure at which the clutch will just begin to carry torque and engage or disengage the related gears at a known applied current, so that this current may be repeated to facilitate simultaneous engagement and/or disengagement of the clutch when necessary.
However, the 50 psi figure was at best an approximation, given the tolerances found in the solenoid valves themselves as well as related hydraulic and mechanical components of the clutching system. It has been found, for example, that some clutches will tend to carry torque at as low as 48 psi valve pressure, while some will require as high as 58 psi valve pressure to begin to carry torque. Moreover, both the valves and the clutches may change over time, due to wear and/or temperature variations. Also, it was most cumbersome and difficult to physically adjust the valve components with the engine and control system in an operating state, to achieve the desired 50 psi adjustment.
Accordingly, we have proposed an automated calibration system in which the relationship between the current to the solenoid operated valve and the point at which the associated clutch begins to carry torque is automatically determined and used to calibrate the control system. This will result in not only a relatively simple calibration procedure, but also in a much more accurate calibration, resulting in an overall smoother, more reliable shifting, particularly when the operation of two clutches is required.